(i) Field of the Invention
The present invention relates to the field of the atmospheres used in heat treatment furnaces. More particularly, it is concerned with atmospheres as afforded by the deoxygenation of an oxygen-containing gas mixture (such as, for example, consisting of air, or a mixture of air and cryogenically obtained nitrogen, or an impure nitrogen produced by the separation of air by permeation or adsorption) by the reaction of this mixture with hydrocarbon in a catalytic deoxygenation reactor.
These atmospheres usually contain a majority species which is generally nitrogen, which may be supplemented, depending on the type of heat treatment performed and the nature of the treated materials, with additional more or less active species such as H.sub.2, CO, H.sub.2 O, CO.sub.2, or hydrocarbons.
(ii) Description of Related Art
In EP-A 482,992 the applicant proposed a catalytic method for preparing such heat treatment atmospheres in which the reaction of impure nitrogen+hydrocarbon is carried out over a precious metal-based catalyst at a temperature between 400.degree. C. and 900.degree. C.
Studies pursued by the applicant on this subject showed that the performance of this process required improvement, particularly in the following areas:
improvement in the composition of the prepared atmosphere in order to decrease when necessary the concentration of oxidizing species and decarburizing species such as CO.sub.2 and H.sub.2 O; and PA1 improvement in the operating conditions for the catalyst for the purpose of extending its life. PA1 better control of the reactions taking place within the catalytic reactor; PA1 a more favorable temperature distribution within the catalyst, which functions to prolong its life and improve its performance. PA1 CH.sub.4 +O.sub.2 .fwdarw.CO.sub.2 +2H.sub.2 PA1 CH.sub.4 +2O.sub.2 .fwdarw.2H.sub.2 O+CO.sub.2 PA1 CH.sub.4 +H.sub.2 O.fwdarw.CO+3H.sub.2 PA1 CH.sub.4 +CO.sub.2 .fwdarw.2CO+2H.sub.2 PA1 i) The heat introduced by the reactor's electric heating resistances naturally has a tendency to rise from the bottom of the reactor toward the top of the reactor (natural convection). PA1 ii) Moreover, this heat, which thus accumulates in the top part of the reactor, in fact accumulates in the zone where the exothermic reactions that consume little energy occur, which as a consequence does not favor the endothermic reactions which as previously noted are essentially localized in the lower part of the reactor. PA1 results in a more homogeneous temperature profile within the catalyst, thus limiting the formation of hot spots; PA1 results in a lowering of the amounts of carbon dioxide and water vapor in the prepared atmosphere; and PA1 all other operating conditions being held the same, results in the possibility as desired of lowering the setpoint for the catalyst heating temperature by tens of degrees, which unquestionably represents an economic advantage. PA1 the heat treatment atmosphere exiting the catalytic reactor, between exit from this reactor and arrival of the atmosphere at the use location or at a storage location: PA1 the oxygen-containing first gas mixture, before its entry into the bottom of the catalytic reactor. PA1 a source of an oxygen-containing first gas mixture; PA1 a source of a hydrocarbon-containing second gas mixture; PA1 a catalytic reactor for gas deoxygenation; PA1 an inlet conduit system suitable for supplying the catalytic reactor with the first gas mixture and second gas mixture; PA1 an outlet conduit system suitable for removing from the catalytic reactor the heat treatment atmosphere resulting from the reaction in the reactor between the first gas mixture and the second gas mixture; PA1 which is characterized in that the catalytic reactor is incorporated into the installation in substantially vertical position, and in that the inlet conduit system is connected at its downstream end with the bottom of the reactor and the outlet conduit system is connected at its upstream end with the top of the reactor.